1. Field of the Invention
The present invention relates to somatic cell gene transfer methods for mimicking one or more effects of a drug candidate compound. In one aspect, the methods mimic the effect of a drug candidate compound with potential to potentiate or suppress activity of a selected target molecule. In another aspect, the methods provide means of identifying a molecular target for the drug candidate compound. The present methods have a variety of uses including providing identified molecular targets for use in drug screens.
2. Background
Eukaryotic organisms include a variety of cells, tissues and organs that react to stimuli. Cell pathways have evolved to react to the stimuli. The cell pathways generally include molecules such as receptors, pore- or channel-forming proteins, enzymes, growth factors, differentiation factors, messenger molecules, immunocompatibility factors and certain structural molecules. See generally Alberts, B. et al. (1989) in The Molecular Biology of the Cell 2nd ed. Garland Publishing, Inc. New York; and Kandel, E. R. et al. (1991) in Principles of Neuroscience 3rd ed. Appleton & Lange, Norwalk, Conn.
In particular, specified cell pathways include complexes of ion channel proteins that propagate charge between certain electrically responsive cells. See e.g., Hille, B. (1991) Ionic Channels of Excitable Membranes, 2 ed. Sunderland, Mass. Sinauer.
The cell pathways play a major role in the function of eukaryotes. Accordingly, there have been substantial efforts toward identifying drugs with therapeutic capacity to modulate the cell pathways in a predictable manner.
Several traditional approaches have been developed to detect drugs with therapeutic capacity to modulate the cell pathways.
For example, “natural products testing” is one such approach. In a typical approach, material is obtained from a biological source and then screened for a pre-determined activity. Positive results are usually followed by purification of the material from the biological source and identification of the molecule(s) responsible for the activity. See e.g., Hardman et al. (1996) eds. in Pharmacological Basis of Therapeutics 9th ed. McGraw-Hill.
Other approaches encompass what is sometimes referred to as “synthetic chemical testing”. In this approach, a promising lead compound is synthesized and optionally derivatized by specified chemical manipulations. Typically, there exists substantial knowledge with respect to the structure and function of that lead compound as well as the manipulations necessary to develop a drug candidate compound from the lead compound. See e.g., Hardman et al. supra.
However, such traditional approaches for developing drugs have recognized shortcomings.
For example, natural products testing can require access to a large variety of organisms many of which may be rare or produce drug candidate compounds in limiting quantities. Labor and time investments are typically substantial. In most cases, there is incomplete knowledge as to the structure and function of the compounds. Even less is usually known about the molecular targets of such compounds.
Approaches relying on synthetic chemical testing have suffered from related shortcomings. For example, chemical manipulations required to make a drug candidate compound can be labor intensive and require several years of research effort. In many instances, development of a promising compound has proceeded without adequate knowledge of the molecular target(s) of that compound.
More generally, the traditional approaches have been hampered by inadequate knowledge of the molecular targets of many drug candidate compounds. That lack of knowledge can negatively impact efforts to identify and develop the compounds. By focussing on the target molecule of the compound, the traditional approaches may miss opportunities to detect a variety of promising compounds.
In particular, a promising drug candidate compound may go undetected in a traditional approach if that compound cannot interface with a molecular target. For example, a compound with unsuitable solubility or stability may be discarded in a traditional screen even though that compound can potentiate or suppress activity of a key target molecule such as a protein.
There have been recent attempts to circumvent or at least reduce the need to identify the molecular targets of drug candidate compounds. In general, screens have been implemented that substantially increase the diversity of known lead compounds. The objective has been to increase the number of lead compounds in the hope of identifying a compound of interest.
For example, combinatorial chemistry is one approach for substantially increasing the diversity of lead compounds. The technique is premised on the general assumption that production of large libraries of lead compounds and particularly lead compound derivatives, will provide a pool from which can be selected a significant number of drug candidate compounds. See e.g., Brenner et al. (1992) PNAS (USA) 89: 5381 Nielsen et al. (1993) J. Am. Chem. Soc. 115: 9812 and references cited therein.
More recently, there have been efforts to integrate computer-assisted modeling techniques and combinatorial chemistry into a unified screening approach for detecting drug candidate compounds. The approach is sometimes referred to as “targeted diversity” or “rational drug design”.
However, combinatorial chemistry and targeted diversity suffer from significant drawbacks. For example, although these approaches have potential to increase pools of drug candidate compounds, implementation is not always cost and time effective. For example, these screening techniques are often negatively impacted by a lack of understanding of molecular targets of the lead compounds.
Accordingly, in many instances the molecular targets of the drug candidate compounds are unknown, thereby potentially stalling development of future compounds. Efforts to improve existing compounds may suffer a related fate.
There has been substantial research efforts toward identifying ion channels such as potassium channels. The ion channels represent a highly diverse family of proteins of particular pharmacological interest. The proteins are known to form multimeric membrane complexes. See e.g., Deal, K. D. et al. (1996) Phys. Rev. 76: 49; Rudy, B. (1998) Neuroscience 25: 729.
Specifically, certain ion channel proteins have been reported to be involved in human diseases such as epilepsy, heart failure and inherited long QT syndrome. See e.g., Bassett, A. L., et al. (1994) Circ Res 75:296; Tsaur, M. L., et al. (1992) Neuron 8: 1055; Kaab, S., et al. (1996) Circ Res 78 (2), 262–73; and Good, T. A., et al. (1996) Biophys. Journal 70: 296.
Selective gene suppression is an approach for understanding protein function. For example, antisense and dominant negative methodologies have been used to manipulate function of certain ion channel proteins. See e.g., Wagner, R. W. (1995) Nature Medicine 1: 1116.
It thus would be useful to have assays that mimic the effects of drug candidate compounds and particularly those compounds with capacity to potentiate or suppress activity of a specified target molecule. It would be particularly desirable to have in vitro assays that can identify the target molecule without complete knowledge of the compound. It would be further desirable to have in vitro assays that effectively mimic diseases or disorders impacted by the target molecule and the compound.